1. Field of the Invention
The present invention is generally in the field of electrical circuits. More particularly, the invention is in the field of phase locked loops.
2. Related Art
Phase locked loops are often used as frequency synthesizers in applications, such as communication systems, that require a precise signal frequency. The typical components of a phase locked loop include a phase detector, a frequency-controllable oscillator, and a loop filter. Phase detectors, such as a charge pump phase detector and a sample-and-hold phase detector, are commonly implemented using analog circuitry. However analog phase detectors suffer from the traditional limitations of analog circuitry, such as variation with process, temperature dependence, sensitivity to substrate coupling, and limitations caused by parasitics.
Various approaches to digital phase detection have been attempted to overcome the above limitations of phase detectors that use analog circuitry. However, conventional digital phase detectors often require multi-Gigahertz clocks or other types of circuit blocks that are undesirable.
Thus, there is a need in the art for a digital phase detector for a phase locked loop that overcomes the deficiencies of conventional phase detectors.